veth: Fix -Wformat-truncation

veth: Fix -Wformat-truncation

Provide a precision hint to snprintf() in order to eliminate a
-Wformat-truncation warning provided below. A maximum of 11 characters
is allowed to reach a maximum of 32 - 1 characters given a possible
maximum value of queues using up to UINT_MAX which occupies 10
characters. Incidentally 11 is the number of characters for
"xdp_packets" which is the largest string we append.

drivers/net/veth.c: In function 'veth_get_strings':
drivers/net/veth.c:118:47: warning: '%s' directive output may be
truncated writing up to 31 bytes into a region of size between 12 and 21
[-Wformat-truncation=]
     snprintf(p, ETH_GSTRING_LEN, "rx_queue_%u_%s",
                                               ^~
drivers/net/veth.c:118:5: note: 'snprintf' output between 12 and 52
bytes into a destination of size 32
     snprintf(p, ETH_GSTRING_LEN, "rx_queue_%u_%s",
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       i, veth_rq_stats_desc[j].desc);
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>